As ever the devil is in the detail, but I would hazard a guess that after wearing full PPE for a shift you are dripping in sweat and the temptation to mop your brow when unsuiting is almost irresistable.
Conjecture at present centres around the use of goggles rather than ful face shield as being the weakness in PPE allowing infection of workers. What is clear is that the carers need to be very careful with it.
There is actually a reasonable question hiding in here. Flies are everywhere in the tropics and attracted to extreta from either end. It would therefore seem likely that they might well be local vectors unless the flies digestive enzymes destroy the virus quickly. My guess is that the tiny contamination delivered by a fly to normal bare skin will dry out and digestive enzymes kill the virus before it infects.
The virus is reported to be unusually large - just big enough to see with an optical microscope and fairly fragile killed by dilute bleach.